1. Field of the Invention
This invention relates generally to controls for accessories attached or mounted to vehicles and more specifically to a cab mounted control for controlling a high current power source for an electric motor which drives an accessory such as a spreader for sand or salt that is coupled to a vehicle.
2. Description of the Related Art
There are many devices that are coupled with a vehicle that require a separate motor to control and operate the device. For instance, a spreader is often mounted on a vehicle to aid in the deposition of granular material such as salt, seed, fertilizers, chemical agents, sand or the like onto a surface as the vehicle travels over it. The spreader is connected to a material supply bin, which is usually gravity fed. As the material falls through the spreader, its is distributed by an auger or similar driving device. The auger is powered by an electric motor which is controlled by the operator in the cab of the vehicle. The operator can start, stop and control the speed of the spreader by so controlling the motor. The speed of the spreader controls the distribution characteristics of the material being spread.
Traditionally, the electric motor requires a relatively high current power source to adequately drive the spreader. Therefore, the motor control circuitry employed must be able to handle such a high current load. Obviously, any type of circuitry capable of handling such a level of current is appropriate. Generally, the power control circuit is mounted in the cab of the vehicle. The operator then actuates a control which will turn on, turn off and vary the speed of the electric motor by varying the amount of current which ultimately reaches the motor.
While this arrangement provides all of the necessary control the operator may require, it also creates several areas of concern. In order to make such an arrangement functional, relatively heavy gauge wire must be run through the firewall of the vehicle and into the cab. In and of itself, this is a modification which many vehicle owners may be hesitant to make as a correspondingly large hole must be cut. Furthermore, the cab and spreader are usually located on opposite ends of the vehicle. As such, a long length of this heavy gauge wire must be utilized. This adds significantly to the cost of such a system. In order to locate the power control circuitry remotely from the motor and driver device, rather large and very expensive high current handling electrical plugs must be utilized, further increasing the overall cost. These plugs are used to couple the high current wire to a control box that contains the MOSFET and also to couple the wire to a junction with the electric motor. In addition, the length of the wire reduces the efficiency of the system due to the voltage drop-off encountered. Finally, the size of the wire makes it difficult to conceal. As such, the exposed wire is subject to abrasions and inadvertent cutting.
The most significant concern, however, is the relatively large amount of heat that is generated by a MOSFET (or similar component) located within the cab of a vehicle, when handling high current loads. The heat generated by the control circuitry represents a fire hazard and severely limits the design parameters available during installation. Typically, the cab mounted circuitry occupies almost 2 square feet of space. It is difficult to place such a large device within the cab of a vehicle because the heat produced will often adversely affect the surrounding components. A large number of the items within the cab are made of plastic and are thus subject to melt. Wiring proximate the control circuit can also be damaged by the heat and thus short circuit. This causes obvious mechanical/electrical problems and also creates a risk of fire. If the circuitry can be mounted in a location that does not affect components in the cab, it will prevent the operator from being able to fully utilize the cab. That is, anything brought into the cab must be carefully placed to avoid contact with the control circuit.
As such, the heat generated by previous power control circuits is of significant concern. There has been no way to minimize this heat generation as those components which can handle the required current levels must necessarily dissipate this heat in some manner. Presently, such systems must simply be installed within the cab of the vehicle, in a location which hopefully minimizes the exposure of sensitive elements to the high levels of heat generated. The heat is simply allowed to dissipate into the surrounding air. Such installation presumes that the airflow within the cab will be sufficient to prevent the control circuitry from overheating. This is often incorrect, and as a result, the control circuitry may be prone to overheating, thus amplifying the above described concerns. Since the space inside the cabs of vehicles is so limited, the placement of the control is extremely problematic. As a result, vehicle owners must risk serious damage to their vehicles and forego the use of significant amounts of space within the cab in order to simply control an attachment which is mounted on the vehicle.
Therefore, there exists a need to provide an accessory control unit for high current drawing vehicle accessories that is electrically efficient and thermally isolated.